The present invention relates to mobile telecommunication systems, and more particularly to methods and apparatuses that determine when and/or what measurements user equipment (UE) in a telecommunication system will make of its surrounding environment.
Digital communication systems include time-division multiple access (TDMA) systems, such as cellular radio telephone systems that comply with the GSM telecommunication standard and its enhancements like GSM/EDGE, and Code-Division Multiple Access (CDMA) systems, such as cellular radio telephone systems that comply with the IS-95, cdma2000, and Wideband CDMA (WCDMA) telecommunication standards. Digital communication systems also include “blended” TDMA and CDMA systems, such as cellular radio telephone systems that comply with the Universal Mobile Telecommunications System (UMTS) standard, which specifies a third generation (3G) mobile system being developed by the European Telecommunications Standards Institute (ETSI) within the International Telecommunication Union's (ITU's) IMT-2000 framework. The Third Generation Partnership Project (3GPP) promulgates the UMTS standard. This application focuses on WCDMA systems for economy of explanation, but it will be understood that the principles described in this application can be implemented in other digital communication systems.
WCDMA is based on direct-sequence spread-spectrum techniques, with pseudo-noise scrambling codes and orthogonal channelization codes separating base stations and physical channels (user equipment or users), respectively, in the downlink (base-to-user equipment) direction. User Equipment (UE) communicates with the system through, for example, respective dedicated physical channels (DPCHs). WCDMA terminology is used here, but it will be appreciated that other systems have corresponding terminology. Scrambling and channelization codes and transmit power control are well known in the art.
FIG. 1 depicts a mobile radio cellular telecommunication system 100, which may be, for example, a CDMA or a WCDMA communication system. Radio network controllers (RNCs) 112, 114 control various radio network functions including for example radio access bearer setup, diversity handover, and the like. More generally, each RNC directs UE calls via the appropriate base station(s) (BSs), which communicate with each other through downlink (i.e., base-to-UE or forward) and uplink (i.e., UE-to-base or reverse) channels. RNC 112 is shown coupled to BSs 116, 118, 120, and RNC 114 is shown coupled to BSs 122, 124, 126. Each BS serves a geographical area that can be divided into one or more cell(s). BS 126 is shown as having five antenna sectors S1-S5, which can be said to make up the cell of the BS 126. The BSs are coupled to their corresponding RNCs by dedicated telephone lines, optical fiber links, microwave links, and the like. Both RNCs 112, 114 are connected with external networks such as the public switched telephone network (PSTN), the Internet, and the like through one or more core network nodes like a mobile switching center (not shown) and/or a packet radio service node (not shown). In FIG. 1, UEs 128, 130 are shown communicating with plural base stations: UE 128 communicates with BSs 116, 118, 120, and UE 130 communicates with BSs 120, 122. A control link between RNCs 112, 114 permits diversity communications to/from UE 130 via BSs 120, 122.
At the UE, the modulated carrier signal (Layer 1) is processed to produce an estimate of the original information data stream intended for the receiver. The composite received baseband spread signal is commonly provided to a RAKE processor that includes a number of “fingers”, or de-spreaders, that are each assigned to respective ones of selected components, such as multipath echoes or streams from different base stations, in the received signal. Each finger combines a received component with the scrambling sequence and the appropriate channelization code so as to de-spread a component of the received composite signal. The RAKE processor typically de-spreads both sent information data and pilot or training symbols that are included in the composite signal.
In cellular telecommunication systems, such as but not limited to the UMTS, there is a trade-off with respect to how often a UE should measure its surrounding environment, as well as the extent of those measurements. The more frequently a UE measures and keeps track of the surrounding environment (e.g., neighboring cells), the lower the possibility of experiencing loss of coverage, missing incoming calls, and the like. However, the more a UE actually measures, the more power it consumes. Since, more often than not, UEs are operated on battery power, higher power consumption associated with measurement activities leads to undesirable effects, such as lower standby time.
In some telecommunication systems, such as WCDMA systems, there exist measurement related threshold values (e.g., Sintrasearch, which is an optional parameter broadcast by the network that specifies the threshold (in dB) for intra frequency measurements; and QqualMin, which is a mandatory parameter broadcast by the network that defines the minimum required quality level (in dB) in the serving cell) that can optionally be broadcast by the network (NW) to the UEs in a cell. The UE may compare the measured signal quality of its received signal to the received threshold value(s), and based on this comparison stop performing measurements on the surrounding environment if the received signal quality of the cell currently camped on is above the received threshold value(s).
In some other cases, UE vendors have implemented their own hard-coded threshold values based on, for example, characteristics of their particular receiver blocks.
There are several problems with the existing implementations. For example, in some cases, such as the one described above in which there is a possibility of conveying measurement threshold values from the network to the UEs, network operators do not want to risk having the UEs measure too infrequently and consequently losing coverage or missing calls. The loss of services to UEs is both inconvenient and possibly vexatious to users and may result in a substantial loss of goodwill to the operator of the mobile network. Hence, such thresholds are either not sent at all or are set to such levels that they ensure that the UE will measure rather often, even under circumstances in which such measurement is totally unnecessary. In the most common cases, the UE normally performs its measurements during its Discontinuous Reception (DRX) cycles. That is, when not being operated by its user, the UE is normally in a sleep mode, with its radio turned off. However, at such DRX cycles the UE might receive messages and hence has to turn on its radio and scan some channels. As the radio is turned on anyway, the UE might coordinate its operations so that it performs its measurements during these occasions. However, many of these measurements are unnecessary if the UE is in a stable environment (e.g. when the UE is lying still on a table) because no new information would be obtained from such measurements.
In some other cases, the UE vendors have implemented their own hard-coded thresholds. These thresholds are often developed in a lab environment or by experiments performed in some real environment and are tightly coupled with the radio characteristics of the specific UE. The problem in such cases is the inability to adapt these thresholds to the real surrounding environment.
All these unnecessary measurements drain the battery power and affect the standby time of the UE.